Avalanche diode

An avalanche diode is a semiconductor device specially designed to work in reverse voltage. In these lightly doped diodes, when the reverse bias voltage reaches the value of the breakdown voltage, the electrons that have jumped to the conduction band due to the effect of temperature are accelerated due to the electric field, increasing their kinetic energy, so that when they collide with valence electrons they are released; these, in turn, accelerate and collide with other valence electrons, also releasing them, producing an avalanche of electrons whose effect is to increase the current conducted by the diode with hardly any increase in voltage.

The Zener diode is also designed to work in reverse, although the breakdown mechanism is different from the one discussed here.

General uses

Protection

The typical application of these diodes is the protection of electronic circuits against surges. The diode is reverse connected to ground so that, as long as the voltage remains below the breakdown voltage, it will only be passed through by the very small reverse saturation current, therefore interference with the rest of the circuit will be minimal.; for practical purposes, it is as if the diode did not exist. When the circuit voltage increases above the breakdown value, the diode begins to conduct, diverting the excess current to ground, avoiding damage to the circuit components.

RF Noise Sources

Avalanche diodes generate radio frequency noise and are therefore commonly used as noise sources in radio frequency equipment. They are also used as noise sources in antenna analyzers and as white noise generators.